1. Field of the Invention
This invention relates in general to toggle memories and specifically to writing to toggle memories.
2. Description of the Related Art
A memory cell is a storage unit of a memory that stores a bit of data. Toggle memories are memories having storage cells whose logic state is written by toggling the state stored in the cell from either a first state to a second state or from the second state to the first state. With toggle memories, if a particular logic state is desired to be stored in a cell, the present state of the cell is first read to determine whether the present state matches the desired state. If the present state does not match the desired state, then the cell is toggled to change the state to match the desired state. If the present state matches the desired state, then the cell is not toggled. Accordingly, each write cycle of a toggle memory cell requires a read of that cell.
One type of toggle memory is a type of magnetoresistive random access memory (MRAM) that includes cells using multiple free magnetic layers that toggle between states when subjected to a sequence of magnetic pulses along two directions. One example of such a memory is set forth in U.S. Pat. No. 6,545,906, which is hereby incorporated by reference in its entirety.
With some types of MRAM cells, the state of the cell is differentiated by the resistance of the magnetic tunnel junction of the cell. In a first state, the resistance is relatively low. In a second state, the resistance is relatively high. Because reading a cell requires a differentiation of resistance values, reading a cell can be relatively slow as compared to the toggling operation.
What is needed is an improved method for writing values to an toggle memory.
The use of the same reference symbols in different drawings indicates identical items unless otherwise noted. The figures are not necessarily drawn to scale.